FIG. 11 is a partial cross-sectional view of a portion of prior art torque converter 400.
FIG. 12 is a partial front view of the portion of torque converter 400 of FIG. 11 generally along line 12-12 in FIG. 11 with portion P1 of a cover plate cut away. The following should be viewed in light of FIGS. 12 and 13. Torque converter 400 includes cover 402 arranged to receive torque, vibration damper 404, and torque converter clutch 406. The vibration damper includes springs 408 at least partially surrounded by cover plate 410. The clutch includes piston plate 412, drive plate 414, and friction material 416. In some cases caps 418 are placed on the ends of the springs. Portion 414A of the drive plate is axially disposed between the piston plate and the cover and a plurality of portions 414B is circumferentially located between the springs.
In a torque converter, the torque converter clutch by-passes the fluid coupling of the pump and turbine when the differential pressure is increased on the “apply” side of the piston to close the clutch (clutch lock-up). During lock-up the clutch may be permitted to slip (spin at a specified differential speed to the cover temporarily or indefinitely. Drive plate 414 is used to transmit torque from the cover to springs 408 when piston 412 closes the clutch.
It is necessary for drive plate 414 to remain centered, or only minimally off-center, with respect to axis A for the torque converter, to ensure proper functioning of the clutch and the torque converter. The drive plate is not fixed to the cover or the piston, thus, the drive plate relies on contact with springs 408 for centering. When the torque converter is at rest, springs 408 are in the centered position shown in FIGS. 11 and 12. Compressive engagement of the driving plate and the springs determines the position of drive plate with respect to axis A for the torque converter. When torque converter 400 is at rest (not rotating), portions 414B are either in compressive engagement with the springs, or are separately from the springs by a narrow gap. In the latter case, once the clutch is closed and the drive plate begins rotating and transmitting torque from the cover (for example, in direction C) to the damper, the drive plate engages the springs. Thus, end E of portion 414B is engaged with spring 408A at rest or begins to engage and compress spring 408A in direction C when torque is applied and this engagement centers the drive plate.
As the damper begins to rotate at higher speed, springs 408 are forced outward by centrifugal force, for example in direction R1. When rotation exceeds a threshold value, the springs displace radially outward enough to engage surface S of the cover plate. Thus, the springs are being compressed at the same time as being pushed against surface S, which creates resistance as the springs are pushed along the surface by the compression. When the clutch is disengaged and the cover plate continues to rotate with sufficient speed, the resistance and the continued centrifugal force prevent the spring from decompressing. Thus, the spring remains displaced radially outward and the springs are no longer able to center the drive plate properly.
It should be understood that misalignment of the drive plate, or lack of centering of the plate, with respect to axis A can be either radially inward or radially outward (with respect to axis A), depending on the point of reference. FIG. 12 shows a view of the top portion of a cross-section in FIG. 11. If surface OC on the outer circumference of the drive plate displaces a certain distance in direction R2 (moves away from the axis), a point on the inner circumference of the drive plate, 180 degrees from point OC, will move toward the axis by the same distance. Thus, both radially outward and radially inward misalignment are present at the same time.
In one instance, the drive plate is displaced off-center with respect to A by the displacement of the springs and the springs are unable to relax as noted above. That is, the drive plate is in compressive engagement with the springs and the drive plate is “dragged” out of the desired alignment by the displacement of the springs. When the damper speed is reduced enough, the springs will relax; however, since the ends of the springs and ends E are no longer centered, end E is caught between the end of the spring and the portion of the cover at the end of the spring, for example, surface S in portion P2.
In another instance, the clutch is opened, the drive plate is displaced off-center by the displacement of the springs, and the springs are unable to relax as noted above. When the clutch is re-applied, friction material 416 may be damaged by the misalignment of the drive plate with axis A. Or, due to the misalignment with axis A or the catching of the drive plate in portion P2, there may be interference preventing the clutch from closing.